1. Field of the Invention
The invention relates to an apparatus for the arching of glass sheets heated to the softening temperature comprising a plurality of movable transport rods for the planar glass sheet which form a horizontal support surface and a plurality of forming elements which are adjustable to the desired contour of the glass surface to be arched.
2. Description of the Prior Art
From German patent specifications 1,679,961 and 2,331,584 apparatuses for doming or arching glass sheets or panes at softening temperature are known in which the arch shape is constituted by means of bent rods. Each rod can be pivoted about an axis extending through its two ends. On such pivot movement, an arching or curving of the glass sheet results which depends on the shape of the rod. If gravity is not adequate for the necessary change of shape, additionally a bending force can be obtained by pressing the sheet against a counter form or against counter rollers which are formed similarly to the forming rods. A disadvantage with such apparatuses is the problem regarding the exact maintaining of the position of the bending axis, because there is no possibility of guiding the edges. Moreover, apparatuses of this type can only be used to a limited extent for architectural glass because in this case it is not possible to operate with a constant usually cylindrical radius of curvature, as for example in the case of the side windows of automobiles; instead, a changing radius of curvature is required. This radius of curvature is usually substantially smaller than in cylindrically curved trays or sheets for automobile glazing in which the radii are usually more than 800 mm. In contrast, the radii of curvature with architectural glass may sometimes only be 100 to 300 mm. These radii of curvature cannot be achieved with the known apparatuses. Moreover, often a cylindrical curvature has to be generated only in one strip and the surfaces of the glass sheet bordering said strip remain planar. Such glass sheets are used in the architectural area for example for forming outer corners in glass facades or also for bar glazing, shower cabins, etc. Such glass sheets cannot be curved with the known apparatuses either.
Further known apparatuses, as described for example in BE-2,621,902, are also not suitable for making such glass panes or sheets. In this apparatus the glass sheet runs onto upwardly convexly curved forming rods whose insert magnitude of the bending line increases in the passage direction. In this case, the only bending force is gravity. Theoretically, this apparatus could be used for producing the described bends with two straight legs and an internal curvature. However, in practice almost insurmountable difficulties would occur with regard to the guiding of the glass sheet. In addition, to obtain the planar legs for each necessary curvature a separate set of complicatedly configured forming rods would be required.
U.S. Pat. No. 3,856,499 discloses an apparatus for arching glass planes having two sets of forming rollers which are arranged vertically above each other in the vertical direction and comprise concave and convex surfaces. The two forming roller sets can be displaced relatively to each other so that the glass sheet introduced between the rollers is deformed in a manner similar to that between a pair of forming rollers. Apart from the poor optical quality which is achieved with such a rolling bending method, with narrow radii in this apparatus a great difference arises in the peripheral speed of the rollers with respect to the glass transported between the rolling nip formed by the rollers. Moreover, for each glass sheet form a new forming roller set must be made available and this is disadvantageous with regard to investment costs, resetting expenditure and the like.
The apparatus according to U.S. Pat. No. 3,701,644 has similar disadvantages in the bending of optically satisfactory architectural glasses.
A further apparatus for curving or arching glass sheets heated to softening temperature is known from German patent 2,532,318. In this case the forming rods are constituted by a core and a rotatable driven outer sheath or a sleeve. For transporting the still planar glass sheets into the apparatus the curved forming rods are pivoted into the horizontal position so that a horizontal transport plane arises. For initiating the bending operation the curved forming rods are pivoted downwardly. The actual arching is achieved by raising the entire system upwardly with the forming rods and pressing it against a counter form.
This known principle is also applicable only to relatively large bending radii because for small bending radii the principle of the driven external shell cannot be continuously implemented because on each revolution said shell must participate in the fibre shortening between the external radius and internal radius. Moreover, with this apparatus it is not possible to generate with a universal forming set bendings with a radius of curvature varying transversely of the transport direction and with straight legs. Finally, due to the kinematics of the principle employed the use of this apparatus is also restricted theoretically to relatively large bending radii.
Finally, German patent 3,150,859 and the equivalent European patent 0 114 168 should be mentioned and disclose an apparatus in which the glass sheet to be curved is transported on straight transport rods from a furnace into the bending apparatus. This apparatus comprises a horizontal guide for the glass sheets to be arched. The horizontal surface necessary for the horizontal guiding is formed by transport rods and rollers for the glass sheet to be arched, the transport rods being movable. The known apparatus comprises in an arched region a plurality of forming rods. The forming rods are adjustable to the desired contour of the glass sheet to be arched. For direct arching of the glass sheet a forming apparatus having a pressure apparatus is provided which can apply an application pressure to the centre of the glass sheet to be arched. Whilst the application pressure of the pressure means subject the glass sheet heated to the softening temperature to a central load, the transport rods are moved away vertically downwardly beneath the glass sheet. In this manner, the glass sheet to be arched comes into the region of influence of the forming rods and is pressed by the pressure means onto the forming rods. In this apparatus the transport rods and the forming rods have a core and a rotatable driven outer shell.
A disadvantage of this known apparatus is that the arching of coated glasses is not possible because the pressing means formed as pressure roller and coming into direct contact with the glass surface damages such a coating. Moreover, the production of arched glass sheets with straight legs in the region of which the deformed glass sheet remains planar is not possible because in precisely this region the sheet to be deformed initially rests on the forming rods. The support action of the straight transport rods which could ensure the desired planarity is thus initially lost precisely in this region.